Repair HTTP Cache Vary Key Bugs

The problem

HTTP caches often serve incorrect variants when lookup and store keys disagree or when the Vary header is processed inconsistently. This leads to leaking authenticated content across sessions, serving compressed bytes to legacy clients, or 304 revalidations updating the wrong representation.

What it does

• Identifies discrepancies between cache lookup and storage paths in repository code.
• Normalizes request-header selection for Accept-Encoding, Locale, and Authorization.
• Aligns variant indexing to ensure the cache reconciles Vary headers learned after the origin response.
• Repairs repository-level cache-key construction and tenant boundaries.
• Generates deterministic local test fixtures to verify cache hits and misses across headers.

Frameworks & tools

Works with repository-level code for CDNs, application-level cache adapters, and proxy configurations. Requires access to Read, Edit, and Bash tools.

Why this beats prompting it yourself

Generic prompts often suggest simple TTL changes or cache clearing which mask the underlying logic error. This skill enforces a strict resource register and failure timeline analysis to fix the architectural disagreement between how keys are generated and how variants are stored.

Use cases

• Fixing localized content leaks where one user sees another's language or tenant data.
• Repairing broken 304 Not Modified flows that refresh the wrong cached representation.
• Ensuring identity-encoded clients never receive Gzip or Brotli payloads.
• Standardizing cache key normalization across multi-layer CDN and app architectures.

Known limitations

Does not modify TTL, eviction policies, or origin response headers. Cannot access production environments, live secrets, or deployed state; it is limited to repository-level repairs.